1. Field of the Invention
The present invention relates to a process for the preparation of 5,5′-bi-1H-tetrazolediammonium salts which are lowly toxic, easy to handle, and are useful as gas-generating agents for air bags and as high-molecular foaming agents.
2. Prior Art
An oxaldiimidic acid dihydrazide has a chemical structure expressed by the following formula (1),

A 5,5′-bi-1H-tetrazole (BHT) or a salt thereof has a chemical structure expressed by the following formula (2),

wherein X is a hydrogen atom or a pair of cations.
The following prior arts 1 to 7 have been known for synthesizing these compounds.
(Prior Art 1) Chemical Abstracts Vol. 31, 4985.
This literature describes the synthesis of a 5,5′-bi-1H-tetrazole (BHT) through an oxaldiimidic acid dihydrazide (OAH) by a reaction expressed by the following formula (3),
(Prior Art 2) Journal of Industrial Chemistry Vol. 11, 197–200, (1966).
This literature describes the synthesis of an oxaldiimidic acid dihydrazide (OAH) through an oxaldiimidic acid dimethyl ester intermediate product by a reaction expressed by the following formula (4),
(Prior Art 3) Friedlich DE952,811 (1956).
This literature describes the preparation of a bitetrazole by the reaction of a mole of sodium azide or hydrogen azide with two moles of sodium cyanide or hydrogen cyanide. Its Example teaches the recovery of a 5,5′-bi-1H-tetrazoledisodium salt (BHT.2Na) by condensing the solution after the reaction.
This reaction is expressed by the following formula (5),
(Prior Art 4) Friedlich DE952,811 (1956), U.S. Pat. No. 2,710,297, (1955).
This is the same as the above literature. By using manganese dioxide as an oxidizing agent, there is synthesized a 5,5′-bi-1H-tetrazoledisodium salt (BHT.2Na).
This reaction is expressed by the following formula (6),
(Prior Art 5) Feinberg, J. Org. Chem., 29 (1954) 2021.
There has been described the synthesis of a 5,5′-bi-1H-tetrazolediammonium salt (BHT.2NH3) by a reaction expressed by the following formula (7),
(Prior Art 6) Japanese Patent Application No. 10-374187
The present inventors have proposed the synthesis of a 5,5′-bi-1H-tetrazolediammonium salt (BHT.2NH3) from hydrogen cyanide, sodium azide and hydrogen peroxide water by a reaction expressed by the following formula (8),
in the presence of a catalytic amount of copper sulfate while adjusting the pH of the reaction solution to be 5 to 6.(Prior Art 7) Japanese Patent Application No. 65453/1999.
The present inventors have already proposed the synthesis of a 5,5′-bi-1H-tetrazolediammonium salt (BHT.2NH3) from dicyan and an aqueous solution of sodium azide/ammonium chloride by a reaction expressed by the following formula (9),

According to the prior art 1, two moles of hydrazine hydrate and a mole of dicyan are reacted together in a 50% alcohol aqueous solution, and an oxaldiimidic acid dihydrazide is isolated. The prior art 1, however, is silent concerning the reaction conditions, yields or contents. A trace experiment of the examples showed that the yield of the oxaldiimidic acid dihydrazide was as very low as 44.4%, an unstable intermediate product of 1-cyanoformimidic acid hydrazide, that could become a cause of coloring, remained in the isolated crystals of oxaldiimidic acid dihydrazide and, besides, the content was not enough.
According to this method, next, a 5,5′-bi-1H-tetrazoledisilver salt (BHT.2Ag) is isolated under an acidic condition of nitric acid through the formation of an azide thereof and through the cyclization reaction, followed by the reaction with hydrogen sulfide to remove the product as a silver sulfide out of the reaction system, thereby to obtain 5,5′-bi-1H-tetrazole.
This method, however, needs complex steps and uses an expensive silver salt and toxic hydrogen sulfide, which are drawbacks. A trace experiment of the examples was conducted to isolate the 5,5′-bi-1H-tetrazolediammonium salt (BHT.2NH3). However, the yield of the 5,5′-bi-1H-tetrazolediammonium salt (BHT.2NH3) was as very low as 48.7% on the basis of the oxaldiimidic acid dihydrazide.
According to the prior art 2, a dicyan gas is blown into methanol so as to be reacted therewith in the presence of a sodium methylate catalyst to synthesize an oxaldiimidic acid dimethyl ester and, then, the hydrolyzed hydrazine is reacted with the oxaldiimidic acid dimethyl ester in an ethanol solution, in order to isolate the precipitated oxaldiimidic acid dihydrazide crystals.
At the time of synthesizing the oxaldiimidic acid dimethyl ester which is the intermediate product, however, it becomes necessary to isolate the oxaldiimidic acid dimethyl ester which is the intermediate product by distillation after the insoluble matters precipitated from the reaction solution have been isolated by filtration and to react it with the hydrazine hydrate. Thus, the oxaldiimidic acid dihydrazide is prepared through a long step requiring a cumbersome operation, which is a drawback.
The prior art 3 teaches a method of synthesizing and isolating a 5,5′-bi-1H-tetrazoledisoium salt by using hydrogen cyanide and sodium azide as starting materials. Since the 5,5′-bi-tetrazoledisoium salt is soluble in water, an after-treatment such as condensation is necessary for isolating the compound from the aqueous solution, which is a drawback. The prior art 3 describes that the compound was isolated from the aqueous solution through the after-treatment such as condensation of the 5,5′-bi-1H-tetrazoledisodium salt without, however, teaching yields or physical properties of the isolated compound. A trace experiment of the examples showed an yield of as very low as about 30%.
According to the prior art 4, a 5,5′-bi-1H-tetrazoledisodium salt is synthesized by using sodium cyanide, sodium azide and manganese dioxide as an oxidizing agent and by being cyclized with sodium azide. However, since manganese dioxide is used as an oxidizing agent, a cumbersome after-treatment is required for removing it, which is a drawback.
According to the prior art 5, a 5,5′-bi-1H-tetrazolediammonium salt is isolated by using sodium dinitroacetonitrile, sodium azide and ammonium chloride as starting materials. However, there remain such drawbacks as that the reaction time is long, the yield is low and, besides, the dinitroacetonitrile sodium which is the starting material is not easily available.
Prior arts 6 and 7 involve such a drawback that an expensive sodium azide must be used.